The present invention relates to a floppy disk device, and particularly to a floppy disk device assembly whereof accuracy and strength are improved and the number of parts is reduced.
A conventional example of the floppy disk device assembly will be described referring to FIGS. 7 to 12.
FIG. 7 is a perspective view illustrating an example of the conventional floppy disk device. The floppy disk device is an apparatus for recording data into or reading data from a floppy disk, namely, a diskette of a magnetic recording medium. The floppy disk is installed detachably into the floppy disk device and rotated by a spindle motor of the floppy disk device. A head carriage is driven by a stepper motor on the surface of the floppy disk for positioning a magnetic head which records data into or reads data from the floppy disk.
FIG. 8 is a perspective view wherein are illustrated only the stepper motor, a PM (Pulse Motor) type stepper motor, in this example, and parts supporting the PM type stepper motor of the floppy disk device of FIG. 7.
Referring to FIG. 8, the PM type stepper motor comprises a lead-screw shaft 1, a shaft bearing 4, a housing 5 and driving mechanism provided in the housing 5. At the tip of the lead-screw shaft 1, a pivot bearing 2 is provided for supporting the lead-screw shaft 1.
FIG. 9 is a plane view illustrating an upper side of FIG. 8. The PM type stepper motor is fixed to a base frame 3 with two screws 6, as shown in FIG. 9.
FIG. 10 is a partial magnification of FIG. 9 illustrating the PM type stepper motor and its supporting parts. The pivot bearing 2 is inserted into an opening of a frame pivot-fixture face 3a of the base frame 3 whereto a head carriage seek mechanism is to be installed.
FIG. 11 is a cross section illustrating sections of parts of FIG. 10 cut by a plane including the center axis of the lead-screw shaft 1, and FIG. 12 is a cross section wherein the parts of FIG. 11 are disassembled.
Referring to FIGS. 11 and 12, in a frame motor-fixture face 3b of the base frame 3, there is provided an opening which makes a clearance fit with the external diameter of the shaft bearing 4. Through the opening, the PM type stepper motor is inserted from the tip of the lead-screw shaft 1 so that the tip of the lead-screw shaft 1 fits to pivot bearing 2 by way of a steel ball 12 inserted between them. The shaft bearing 4 is also inserted into the opening until a normal position where the flange of the housing 5 fits to the frame motor-fixture face 3b. The PM type stepper motor is fixed to the frame motor-fixture face 3b at the normal position by screwing the two screws 6 into two screw holes each provided symmetrically and diagonally with each other to the opening so as to tighten the flange of the housing 5 onto the frame motor-fixture face 3b.
In the housing 5 made of magnetic material, there are provided a plate spring 16 for receiving the bottom surface of the lead-screw shaft 1, and a coil assembly consisting of coils 13 and a stator yoke 14. The coil assembly is put into the housing 5 so that each stator of the stator yoke 14 is positioned being separated with a predetermined phase angle from each tooth of housing stator-teeth 5a, which are configured by punching out the magnetic material of the housing 5, for example. The lead-screw shaft 1 whereon a permanent magnet 11 is configured is inserted inside the coil assembly (the coils 13 and the stator yoke 14) and the housing stator-teeth 5a, and then a housing cap 15 made of magnetic material having housing cap stator teeth 15a is put inside of the housing 5. The shaft bearing 4 fixed to the housing cap 15 retains the lead-screw shaft 1 which is inserted through the shaft bearing 4 and pushed to the plate spring 16.
Thus, the PM type stepper motor is assembled and fixed to the base frame 3.
As above described, the PM type stepper motor is fixed to the base frame 3 with the two screws 6, in the conventional floppy disk device. This means that the two components for positioning the lead-screw shaft 1, namely, the pivot bearing 2 and the shaft bearing 4 are each fixed to each different member. Therefore, the axis of the shaft bearing 4 may be shifted form that of the pivot bearing 2 by the error of assembling, that is to say, the correct coaxiality of the lead-screw shaft 1, and accordingly, the correct concentricity of the rotor and the stator of the PM type stepper motor may not be obtained, resulting in variation of the distance between the rotor and the stator.
Therefore, there is a problem that the seeking accuracy of the head carriage may be easily affected by a poor coaxiality of the lead-screw shaft 1, in the conventional floppy disk device.
Another problem of the conventional floppy disk device is that the positioning of the PM type stepper motor may be easily shifted with an unexpected sock or a change of atmosphere such as temperature or humidity, because of the same reason that the PM type stepper motor and the base frame as fabricated separately and fixed together with the two screws 6.
Still another problem is that there are needed many parts, and accordingly, many assembling processes accompanied by a high assembling cost and a high part cost, because the PM type stepper motor and the base frame are fabricated separately.